I pretty much know nothing about saltwater so I don't know exactly how expensive corals are (I have heard of "cheap" ones and prices vary up to really expensive pieces) or how fast they "grow".
Same with freshwater plants, costs vary. Just browse through the for sale section on this forum and see the price range of the plants. You can find stems of certain species for .50 cents to $15 each, bunches from $3 to $20, single plants from $1 to $50+ (just ball park numbers, definitely can be some cheaper or more expensive).
The more expensive ones are more rare and exotic looking while there are cheap that look nice as well. All depends what plants you want, how many you want and how much you are willing to spend. Some are collectors of plants species and would pay top dollar (hundreds) for a single rare plant.
Same with corals/frags/live rock. Even fish costs and driftwood costs. All varies on the person buying.
With that said, you can still make a beautiful scape just using the cheap plants, so it doesn't have to cost much at all to have a nice looking planted tank.
I started this hobby as a fish guy and just recently got into planted tanks. Within these past few months I've spent $150 on Bucephalandra alone and $350+ on various other plants so far (most of them from this forum, best deals hands down most of the time, definitely get a lot more for the money) and I am planning on doing another $100 order in a couple days from now on another site (got some species of plants I want that are currently not available on here).
Me being a fish guy, you don't want to know how much I've spent on fish alone.... not to mention the costs of every other aspect of planted aquariums/this hobby.
This hobby can turn expensive real quick, wish I knew before I started...